Wired radio transmitting system



. R. D. DUNCAN,- JR WIRED. RADIO TRANSMITTING SYSTEM June 8 1926;

Filed Dec. 25, 1925 1 amnion ITED STATES PATENT OFFICE.

ROBERT D. DUNCAN, JR., OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO WIRED RADIO INCL, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE.

WIRED RADIO TRANSMITTING SYSTEM.

Application filed December 23, 1925.

My invention relates broadly to carrier wave transmission systems and more particularly to a nniltiplex polyphase high frequency current transmissioirsystem.

One of the objects of my invention is to provide a highly etlicient system of wired radio broadcasting where a plurality of channels or programs are transmitted simultaneously over the same line wire distribution system without mutual interference.

Another object of my invention 1s to pro- 'vide a polyphase high frequency carried current transmission system where special means are provided for balancing the circuits in such manner that harmonics of the fundamental frequencies are prevented from causing interference .with the reception of a plurality of distinct programs which may be transmitted simultaneously.

Still another object of my invention is to provide a circuit arrangement for a three phase multiplex wired radio transmitter for operating into a three phase electric power transmission system where means are employed for avoiding interference with several channels from all even and all triple frequency harmonics of the fundamental frequencies.

In a wired radio broadcasting system wherein high frequency carrier currents are superimposed upon electric lightlng lines, it has been determined that the generation and use of polyphase high frequency currents for transmission over a polyphase electric power distribution line possesses many advantages over single phase high frequency current operation. In particular three phase high frequency currents would be employed for transmission over a three phase electric powcr system,-of which the latter are the majority of electric power distrlbution systems in the United States.

In a multiplex or multichannel wired radio broadcasting system, that is, a system in which two or more programs are broadcast simultaneously, and each rogram or channel confined to given and different frequency hands, it has further been deter- 'lllll'led that the existence of harmonics of the fundamental frequencies of the different channels exercises a very disturbing effeet in the various receivers by virtue of their beatin with each other and with the I different func-amentals. For example, if in a two channel broadcasting system the two over the lines.

Serial- No. 77,289.

fundamental frequencies are respectively 30,000 and 45,000 cycles, i. e., displaced by a frequency approximately above audibility, the second and third harmonics are respectively 60,000, 90,000 and 90,000, 135,000 cycles. It will be observed that the two second harmonics will beat to form 30,000 cycles and the two third harmonics will beat to form 45,000 cycles. These beat frequencies will cause interference with the funadmental frequencies of the same values. Other harmonics may beat to form much lower frequencies which are Within the range of audibility and will thus cause interference. If three or more channels are operated, the resulting interference grows very serious. It will be noted therefore, that a fundamental transmission problem in multiplex wired radio broadcasting isthat of elimination of harmonics of the fundamental transmitting frequencies. In operating two or more transmitters into a pair of transmission lines orinto polyphase'transmission lines, it is to be noted that the different transmitters may be connected either in parallel or bridged across the lines or may be coupled or connected in series with the lines. It has been determined that parallel operation is disadvantageous in a number of respects, principal among which is that elaborate multiply tuned circuits or filter circuits have to be employed to prevent the establishment-of large circulating currents in the local transmitting circuits which would otherwise exist, and which seriouslyreduced the high frequency power available for transmitting The use of such circuits is complicated and expensive, and results in a serious loss of power by virtue of the resistance of the inductive and capacity elements. The series operation of a plurality of transmitters into transmission lines in accordance with the principles of my invention is free from these disadvanta es.

My invention will be more clear y understood from the following specification with particular reference to the accompanying drawing which shows diagrammatically the three channel three phase wired radio transmission system embodying the principles of my invention.

Referring to the drawing i1 detail, reference characters 1, 2, 3 represent three sources of modulated three phase high frequency current operating respectively at frequencies f f f (viz frequencies whennot modulating) Three phase source 1 operates into series connected inductances 47, 5-8 and 6-9, the paired inductances being connected in Y, which in the pairs taken form the primarywindings of input transformers 10-11, 12-13, 14-15. Sinnlarly, source 2 operates into primary inductances 16-19,

.17-20, 18-21 of transformers 22-23,

24-25, 26-27, and source 3 into primary inductances 28-31, 29-32, 30-33, of transformers 34-35, 36-37, 38-39..

Primary coils 4, 5, 6, 7, 8, 9, 16, 1.7, 18, 19, 20, 21, 28, 29, 30, 31, 32, 33 are assumed to be substantially symmetricallly wound and with their magnetic polarities 1n thesame direction. No appreciable coupling is assumed to exist between these primary COllS. Inductively coupled to primaries 4, 16, 28, 7, 19, 31, 5, '17, 29, 8, 20, 32, 6, 18, 30, 9, 21, 33 are, respectively, secondary-inductances 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, which are assumed to be so wound and placed with respect to each other that their magnetic polarities are in the same direction, and to haveno apprecia-ble coupling between the individual inductances. Inductances 40, 41, 42 are connected in series with each other and with the grid of electron tube 58 and ground 64 through biasing battery 65. Similarly. 1nductances 43-44-45, 4647-48, 49-50- 51, 52-53-54, 55-56-57, taken in the order of threes mentioned, are connected in series and respectively with the grids of tubes 59, 60, 61, 62, 63. The filaments of the electron tubes are shown energized by b at teries. The filament of each of the tube pairs, 58-59, 60-61, 62-63 are interconnected respectively, at 66, 67 68 and grounded at 64 to form a point of connection common to each other and to the grid input circuits. The plates 69, 70 of tubes 58, 59 are connected together through capacities 75, 76 and inductances 77, 78. The common point of connection of inductances 77, 78 is grounded at 64 through connections 79. Similarly, plates 71-72, 73-74 are, in the pairs mentioned, connected together through capacities 80, 81 and inductances 82, 83 and capacities 84, 85 and inductances 86, 87. The common points of connection of inductances 82-83 and 86-87 as before are grounded at 64 through connection 7 9. In-

it will be noted, are connected in Y, a preferred form of connect-ion for this invention. Inductively coupled to the inductance pairs 77-78, 82-83, 86-87 are respectively inductances 88, 89, 90, preferably also connected in Y through connection 91. Inductance 88 is connected in series with variable inductance 92, parallel tuned circuits 93, 94, pro- 101, 102, andcondenser 103, to the two re maining conductors of the three phase electric power transmission system, not here shown. Plates 69, 70, 71, 72, 73, 74 receive thelr positive high continuous voltage from source 104 here shown as a battery with negative terminal grounded at 64 and positive terminal connected through high frequency choke coils 105 to the plates.

It will be observed that the circuit shown in the drawing is thatof a three channel, three phase wired radio transmitting system. The three channels respectively have the unmodulated frequencies 7",, f,, f,, derived from the three sources of three phase high fre quency current 1, 2, 3, assumed to be modulated by. the voice or otherwise, by any of the well known means not here shown. Each of these three phase sources operates into a three phase high frequency electron tube power amplifier, the latter of the balanced type. Voltages of the three frequencies f f 7%, are impressed in series with the grid circuits of the tubes. Due to the relatively high input impedance of the power amplifier tubes no special tuning adjustment of the grid circuits of the tubes for the three frequencies f,, f f,, is in general required, though condensers 106, 107, 108, 109, 110,111, 112,11e,1'11,115, 116,117,118,119, 120, 121, 122, 123 connected as shown may be required to assist in increasing the efliciency. The output circuitsof the tubes are connected in the well known balanced manner as shown, and here again, due to the relatively high impedance of the plate circuits no special tuning adjustment is in general required to obtain efficient operation on three different frequencies. The plate inductances are all connected in Y. Theline coupling inductances are alsoconnected in Y.

The input resistances of the electric power transmission lines at the broadcast frequencies may be of the order of 50 ohms and is relatively low. Circuits have to be used therefore, which are capable of simultaneously tuning-the lines to the three frequencies f,, f. i. e., to give to the line circuits minimum impedance for these three frequencies and appreciably high impedance.

to other and widely differing frequenc1es. There are a number of types of circuits which will perform this function.

efiicient in operation.

. the combination of The arrangement of circuits 93, 94, 97,

'98, 101, 102 in conjunction with couevolved by merelyincreasing the number of sources and associated transformer circuits. In the operation of the system of my invention, the multichannel three phase high frequency current transmitter is sub-' stantiallyfree from harmonics and highly The freedom from harmonics is accomplished by suppression of even harmonics, that is 2, 4t, 6, 8 etc, times the fundamental, frequency through the use of the-balan ced type of high frequency power amplifier. The triple fre quency harmonics, that is, 3, 9, 15, 21, 27,

etc., times the fundamental frequency are suppressed by employing a three phase transmitter, Y connected throughout. The remaining harmonics, that is, 5, 7,- 11, 13., 17, etc., times the fundamental frequency are substantially suppressed by'the tuning of the line circuit. The three phase hi h frequency current sources are suitaby modulated in the production of signals and the broadcasting system efficiently operated without interference from undesired harmonics.

Sources 1, 2, sources of modulated three quency current. Intermediate the periods of modulation these sources function as sustained current generators and it is not intended to liinit the scope of this invention to amplification (if polyphase multifrequency modulated high frequency'current. What I claim as new and desire to secure by Letters Patent of the United States is 3 have been referred to as v as follows:

1.. In a wired radio broadcasting system a polyphase electric power transmlssion system, a plurality of sources of polyphase signaling energy, means for impressing said polyphase signaling. energy upon said polyphase tra nsmission system, and means for eliminating harmonic frequencies from said polyphase transmission system.

2. In a wired radio broadcasting-system the combination of a polyphase electric power transmission system, a plurality of phase high Tresources of polyphase signaling energy connected with said polyphase transmission system, and electron tube circuits interposed between said sources and the point of con nection with said polyphase transmission system for suppressing harmonic frequencies from said transmission system.

3. In a. Wired. radio broadcasting system the combination of a polyphase electric powertransmission line, a plurality of poly phase high frequency current transmitters connected'with' said transmission line, and

means interposed between each of said transmitters and said polyphase transmissionline for suppressing harmonic frequencies from said transmission fine.

4. In a wired radio broadcasting system the combination of a polyphase electric power transmission line, a plurality ott channels of high frequency electric energy connected with said polyphase transmission hue, and means locatedin each channel for suppressing harmonic frequencies from said transmission line.

5. In a wired radio broadcasting system the combination of a polyphase electric power transmission line, a plurality of separate sources of polyphase E high frequency signaling energy connected with said polyphase transmission line, and a plurality of electron tube circuits interposed between each of said separate sources of polyphase signaling energy and said polyphase tranmission line for preventing the transmission of harmonic frequencies to said transmission line.

In a wired radio broadcasting system the combination of a polyphase electric power transmissioirline, a plurality of separate sources of high frequency electrical energy, intermediate.circuits positioned between said sources of high frequency electrical energy and said polyphase,transmission line for suppressing harmonic frequencies and preventing the passagethereof into said polyphase transmission line.

7. Ina wired radiobroadcasting system the con'ibination of a polyphase electric power transmission system, a. plurality of sources of polyphase high frequency signaling energy, connections between said sources and said polyphase transmission system, and a plurality of balanced electron tube circuits positioned between each of said sources and said polyphase transmission system for suppressing harmonic frequencies from said transmission system.

8. In a wired radio broadcasting system the combination. of a' polyphase electric power transmission line, a plurality of sources of polyphase high frequency signaling energy, connections between saidv sources and said polyphase transmission line, and a pair of opposed electron tube circuits positioned between each of said sources and said harmonicfrequencies and preventing the polyphase transmission line for balancing ing energy, connections between said sources and said polyphasetransmission line, and sets of electron tube circuits having the input circuits thereof coupled with said sources, and the output circuits thereof coupled with said polyphase transmission line,

v to

said sets of electron tube circuits being ar: ranged to prevent'the transfer ofharmonic frequencies to said polyphase transmission line.

10. In a wired radio broadcastingsystem the combination of a polyphase electric" power transmission system,'aplurality of sources of polyphase high frequency signal ing energy, connections between'said sources and said'polypha'se transmission s'ystennand intermediate circuits included between each of said sources and said polyphase transmission system, said intermediate circuits each including a pair of electron tubes connected in balanced relationship for the suppression of harmonic frequencies from said system.

11. In a wired radio broadcasting system the combination of a polyphase electric power transmission line, a plurality of sources of polyphase signaling energy, connections between said sources and said polyphase transmission line, sets of electron tube circuits included in said connections and balance circuits connected with said electron tube circuits for eliminating harmonic frequencies from said electron tube circuits for preventing the passage thereof to said polyphase transmission line.

12. Ina wired radio broadcasting system the combination of a three phase electric power transmission system, a plurality of sources of three phase high frequency current, a pair of electron tubes positioned bc tween each of said sourcesof three phase high frequency current and said three phase electric power transmission system, said electron tubes each having grid,[filament and plate electrodes, input and output circuits interconnecting said electrodes, with the in put circuits of said tubes coupled with said source andthe output circuits of said tubes coupled with said three phase electric power transmission system, with said circuits ar ranged in such manner that harmonic frequencies are prevented from passing tosaid transmission system. I

13. In a wired radlo broadcast-ing system the combination of a polyphase electric power transmission system, a plurality of sources of polyphase high'frequency signaling their input and output circuits connected in series, with the input circuits coupled with each of said sources and the output circuits coupled with said polyphase transmission systenrin' such manner that harmonic frequencies are suppressed. 4

'14. In a wired radio broadcasting system the combination of a three phase electric pouer -transmission line, a plurality of sources of three phase high frequency current, supply'circuits connected in Y, and connected with eachof said sources,,high frequency amplifiers each including electron tubes having grid, filament and plate electrodes, input and output circ'uitsinterconnecting electrodes, with said input circuits coupled with each of said supplyci'rcuits, the output circuits of each of said amplifiers,being connected in Y and coupled with said three phase transmission line.

15. In a wired radio broadcasting'system the combination of a three phase tran'smission line, independent sources of three phase high frequency electrical energy, a plurality of pairs of electron tube circuits corresponding in number to the number of said sources, said pairs of electron tube circuits having grid and plate circuits connected in series, with said frequency operating in Y connection with said grid circuits, and said plate circuits'operating in Y connection with said three phase transmission line whereby harmonic' frequencies are eliminated fromsaid transmission line.

16. In a wired radio broadcasting system the combination of a three, phase transmission line multiply tuned to the frequencies of a plurality of independent sources, a plurality of separate sources of three phase high frequency current, supply circuits connected with said sources, a plurality of sets of elec-, tron tube circuits corresponding in number to the number of saidsources, said electron tube circuits having grid and plate circuits, with the grid circuits thereof operated in Y and connected with said supply circuits, and the plate circuits thereof connected in Y and connected with said three phase transmission line, whereby even and triple frequency harmonics are eliminated in said wired radio broadcasting system.

17. In a wired radio transmissiousystem the combination. of a three phase electric power transmission system, a-plurality of sources of three phase signaling energy con nected with said three phase transmission system, and electron tube circuits inter osed between said sources and the point'iiif connection with said three phase transmission system for suppressing harmonic frequencies from said transmission system.

7 18. In a wired'radio transmlsslon system the combination of a three phase electric power transmission system, a plurality of 7 sources of three phase high-frequency signaling energy, connections between said sourcesand said three phase transmission system, and a plurality of balanced electron tube circuits'positioned between each of said sources and said three phase transmission" system for suppressmg' harmonic frequen.

' else from said transmission system.

19,; Ina wired radio transmission system the combinationof a three phase electric qpower transmisslon line, a plurality of sources of three phase high frequencysignallng energy, connections between said sourcesand said three phase transmissionv monicfrequencies to said three phase trans mission-line. ROBERT DUNCAN, JR. 

